The present invention relates to a method and an apparatus for finishing a cut surface of a metal work and, more particularly, to a method of finishing smooth a cut surface of a work which was cut from a metal blank by a wire cut discharge process.
Gears and other flat metal works have complicated configurations and require accurate machining are often fabricated by a wire cut discharge process. As well known in the arc, a wire cut discharge process is such that arc discharge is caused between a metal blank and a wire electrode, which is fed from one of two reels to the other, while the metal blank is moved under numerical control in a plane which is perpendicular to the feed direction of the wire, thereby cutting the blank in a desired shape. The recent progress in the numerical control art has made it possible to fabricate products having significantly complicated configurations.
Even with a wire cut discharge process, however, a difficulty has been experienced in finishing a cut surface of a work to a mirror surface. Specifically, although such a process includes second cutting which follows first cutting and is implemented with the discharge of short pulses, this kind of finishing technique leaves undesirable oxide films and degenerated layers on the finished surface due to the discharge. Generally, such oxide films and degenerated layers must be removed because they are detrimental to the physical property of a metal blank.
Therefore, when it is desired to finish a cut surface of a work produced by the above process smooth, the cut surface is usually ground by a grinder of the kind using diamond and other particles or a lapping machine. However, such a prior art finishing method has various drawbacks. When it comes to gears and other components the cut surfaces of which are complicated in configuration, the cut surfaces have to be finished one by one by hand. Because the oxide films formed on the cut surface due to discharge constitute hard surface layers, the manual finishing work not only consumes a prohibitive period of time but also requires expertness.
In light of the above, there has been proposed a finishing method which uses a special electrode the configuration of which is complementary to a cut surface of a work, as disclosed in Japanese Patent Publication No. 54-16079. Specifically, in accordance with such a method, a special electrode having an electrode surface which is complementary to a particular cut surface of a work is positioned to face the latter at a substantially uniform distance. While an electrolyte is fed through a clearance defined between the work and the electrode, current is caused to flow between the work and the electrode via the electrolyte so as to finish the cut surface by electrolytic polishing.
The special electrode scheme as stated above may successfully finish the cut surface smooth by removing oxide films and degenerated layers which are entailed by discharge. However, the use of a special electrode results in the need for extra manufacturing steps. When a gear or like work whose cut surface is complicated in shape is to be finished, the electrode surface of the electrode, too, has to be provided with a complicated shape at the sacrifice of cost. Moreover, various kinds of works which are different in configuration cannot be finished unless electrodes each matching with a particular configuration are prepared. In addition, the finishing work consumes a substantial period of time so long as it depends on such electrolytic polishing.